1. Technical Field
The present invention relates to a toner used for image formation in electrophotographic systems and a preparation method thereof, and in particular to a toner capable of stably forming toner images on paper-used for off-set printing and a preparation method thereof.
2. Related Art
Recently, in the field of imaging technology of electrophotographic systems employing copiers or printers, there has been demand for a technology at a level of precise reproduction of minute dot images at a level of 1200 dpi (dpi: the number of dots per inch or 2.54 cm) along with advancement of digital technologies. Accordingly, reduction of toner particle size has been accelerated and development of a fine-particulate toner has become feasible through chemical toners, also called polymerization toners, leading to faithful reproduction of minute dot images, as described in JP-A No. 2000-214629 (hereinafter, the term, JP-A refers to Japanese Patent Application Publication).
As a result, there has become feasible high-precise image formation of an offset printing level. In addition thereto, rapid accessability capable of achieving print-making without necessity of making a printing plate has expanded business opportunities. Recently, competition with offset printing has kicked off in parts of the field of commercial shortrun printing, as described, for instance, in JP-A No. 2001-240301.
However, an offset printing system and an electrophotographic system differ greatly in design of output paper. For example, paper used for an electrophotography system is designed so as to control resistivity and exclude moisture absorption to attach much importance to electrostatic transferability. On the contrary, paper used for offset printing is designed to enhance affinity to water so as to have the right amount of an aqueous dampening liquid. Accordingly, there was conducted development of paper for offset printing which is also usable in electrophotographic imaging. For instance, paper used for offset printing was proposed, in which an improvement of binding property of cellulose fibers using a water-resistance agent or a water-soluble polymer enabled its use in toner image formation, as described in JP-A No. 10-46498.
However, it was proved that subjecting offset printing paper to a heat treatment caused the variation of the moisture content within the paper, often resulting in curling or a phenomenon such as water vapor blowout at a microlevel, called toner blister. This phenomenon is markedly observed in non-coated paper which was not subjected to a surface treatment. This is due to effects of a hydrophilic compound such as a cationized starch or polyvinyl alcohol which is incorporated to maintain strength of paper fibers.
Glossy coated paper has a glossy surface layer formed of wax exhibiting a melting point of 100 to 160° C. of resin emulsion such as polyacrylamide, so that the surface layer is easily destroyed upon heating at the time of fixing, often resulting in markedly deteriorated glossiness of the white background.
The foregoing problems can be overcome by the use of output paper suitable for each image formation. However, it is not desirable for printing dealers that usable paper is limited by a used apparatus and it rather becomes a barrier blocking printing business.
An electrophotographic image forming technology which can use even offset printing paper, was proposed so that there was desired a toner which can be fixed at a temperature inhibiting generation of water vapor, that is a temperature of less than 100° C. Image formation on both sides of paper is often conducted specifically in the commercial printing field, so that there is desired a toner exhibiting superior image storage stability without causing staining between adjacent printed materials.